During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
It should be recalled that, at one time, industrial fabrics used in papermaking were supplied only in endless form. This is because a newly formed cellulosic fibrous web is extremely susceptible amongst other considerations, to marking by any nonuniformity in the fabric or fabrics.
Despite the considerable technical obstacles presented by these requirements, it remained highly desirable to develop an on-machine-seamable fabric because of the comparative ease and safety with which such a fabric could be installed. Ultimately, the development of fabrics having seams formed by providing seaming loops on the crosswise edges of the two ends of the fabric was achieved. The seaming loops themselves are formed by the machine-direction (MD) yarns of the fabric. The seam is closed by bringing the two ends of the fabric together, by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops to lock the two ends of the fabric together. Needless to say, it is much easier and far less time-consuming to install an on-machine-seamable fabric, than it is to install an endless fabric, on a paper machine.
One method to produce a fabric that can be joined on the paper machine with such a seam is to flat-weave the fabric. In this case, the warp yarns are the machine-direction (MD) yarns of the fabric. To form the seaming loops, the warp yarns at the ends of the fabric are turned back and woven some distance back into the fabric body in a direction parallel to the warp yarns. Another technique, far more preferable, is a modified form of endless weaving, which normally is used to produce an endless loop of fabric. In modified endless weaving, the weft, or filling, yarns are continuously woven back and forth across the loom, in each passage forming a loop on one of the edges of the fabric being woven by passing around a loop-forming pin. As the weft yarn, or filling yarn, which ultimately becomes the MD yarn in the fabric, is continuous, the seaming loops obtained in this manner are stronger than any that can be produced by weaving the warp ends back into the ends of a flat-woven fabric.
A final step in the manufacture of an on-machine-seamable fabric used as a press fabric is to needle one or more layers of staple fiber material into at least the outer surface thereof. The needling is carried out with the fabric joined into the form of an endless loop. The seam region of the fabric is covered by the needling process to ensure that that region has properties as close as possible to those of the rest of the fabric. At the conclusion of the needling process, the pintle which joins the two ends of the fabric to one another is removed and the staple fiber material in the seam region is cut to produce a flap covering that region. The fabric, now in open-ended form, is then crated and shipped to a paper-manufacturing customer.
Industrial fabrics are typically made by the steps of weaving, heatsetting and optional seaming. During the weaving step, a raw material such as, for example, monofilament is typically either woven into “flat,” or rectangular shaped fabric, or else woven as endless, or “loop” fabrics. Thereafter a heatsetting step and then a seaming step usually follow. Seaming requires that opposing ends of the fabric be configured in some fashion to create a seam, such as a pin seam or pin spiral seam.
It is desirable, however, to manufacture an industrial textile fabric in a manner other than the conventional weaving, heatsetting and optional seaming steps.